Hurricane Harvey by the numbers

﻿Hurricane Harvey﻿ drew moisture from the Gulf of Mexico as it slowly drifted over the Houston area.

Photo: HO, Handout

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This August 25, 2017, blended visible/infrared image of Hurricane Harvey obtained from The National Oceanic and Atmospheric Administration shows the storms eye as it nears landfall in the southeastern coast ofThis August 25, 2017, blended visible/infrared image of Hurricane Harvey obtained from The National Oceanic and Atmospheric Administration shows the storms eye as it nears landfall in the southeastern coast of Texas. Harvey has intensified into a powerful category three storm, US meteorologists said on August 25, as the Gulf Coast states of Texas and Louisiana braced for the first major hurricane to hit land since 2005. Harvey, which is set to make landfall late Friday into early Saturday, was packing maximum sustained winds of close to 120 miles (195 kilometers) per hour, the National Hurricane Center said. / AFP PHOTO / NOAA / HO / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "NOAA" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS HO/AFP/Getty Images

It's going to take some time to unpack the totality of Hurricane Harvey.

The wide swath of damage. The displaced people, families and lives. And the toll of it all - financial and emotional.

But as the number of days grows since Harvey sunk much of Houston and the surrounding region in water, there's the percolating realization that what we just experienced is something most living humans have never witnessed. In an age when the term "historic" is overused and often rendered inert, Harvey was a truly historic occurrence.

So how did it happen? How did Harvey go from being a dangerous hurricane to being one of the worst storms to ever reach land?

Well, it's pretty simple: Harvey had nowhere to go. And because of that, the amount of time that Harvey remained over southeast Texas was quite rare, according to Jonathan Belles, a meteorologist with Weather.com.

"Meteorolgically, southeast Texas, at the time, was pretty much a giant stop sign," Belles said. "There were two high pressure systems that wouldn't let Harvey move in any direction. So for three or four days, Harvey pretty much sat there and dumped rain."

A lot of rain. The total of 51.88 inches is a new record for rain totals from one storm in the continental United States. Though, that might change, as Belles said the rain gauge that collected that information was damaged and stopped recording rain amounts.

Typically, tropical storms and hurricanes - their distinctions come from wind speeds - lose gusto once they reach land. But what made Harvey so unique is not only that it was stalled by high pressure systems, which act as "mountains" blocking movement, so to speak, but that it stalled out with part of its body hanging over the Gulf of Mexico.

"Harvey was just hanging out around the Gulf Coast, it had one foot in the Gulf and one foot on land, and (that placement) acted like a conveyor belt pulling water out," said Bernhard Rappenglueck, a professor of atmospheric science at the University of Houston.

Hence, the record precipitation.

The professor says there was also a tropical disturbance, named "Ten," along the Atlantic Coast that helped box Harvey into Texas' Gulf Coast, slowing it to a pace of 2 mph. Once "Ten" left, Harvey began to move faster, and away from Houston.

There could be other contributing factors, Rappenglueck said, such as wet areas underneath Harvey where evaporation added to the moisture collection. But, regardless of how other factors influenced, Harvey was a rare event - from the rainfall totals to the way it reached land, then returned to the Gulf before settling over the Houston metro area.